Method of forming an interconnection element

ABSTRACT

A method of forming an interconnection element. In one embodiment, the interconnection element includes a first structure and a second structure coupled to the first structure. The second structure coupled with the first material has a spring constant greater than the spring constant of the first structure alone. In one embodiment, the interconnection element is adapted to be coupled to an electronic component tracked as a conductive path from the electronic component. In one embodiment, the method includes forming a first (interconnection) structure coupled to a substrate to define a shape suitable as an interconnection in an integrated circuit environment and then coupling, such as by coating, a second (interconnection) structure to the first (interconnection) structure to form an interconnection element. Collectively, the first (interconnection) structure and the second (interconnection) structure have a spring constant greater than a spring constant of the first (interconnection) structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/715,683, filed on Nov. 17, 2003 (U.S. Pat. No. 7,048,548, issued May23, 2006), which is a divisional of 09/473,414, filed on Dec. 28, 1999(U.S. Pat. No. 6,827,584, issued Dec. 7, 2004).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an interconnection element suitable foreffective pressure connections between electronic components.

2. Description of Related Art

Interconnection or contact elements may be used to connect devices of anelectronic component or one electronic component to another electroniccomponent. For example, an interconnection element may be used toconnect two circuits of an integrated circuit chip or to connect anapplication specific integrated circuit (ASIC) to another component suchas a printed circuit board. Interconnection elements may also be used toconnect the integrated circuit chip to a chip package suitable formounting on a printed circuit board of a computer or other electronicdevice. Interconnection elements may further be used to connect theintegrated circuit chip to a test device such as a probe card assemblyor other printed circuit board (PCB) to test the chip.

Generally, interconnection or contact elements between electroniccomponents can be classified into at least the two broad categories of“relatively permanent” and “readily demountable.”

An example of a “relatively permanent” contact element is a wire bond.Once two electronic components are connected to one another by a bondingof an interconnection element to each electronic component, a process ofunbending must be used to separate the components. A wire bondinterconnection element, such as between an integrated circuit chip ordie and inner leads of a chip or package (or inner ends of lead framefingers) typically utilizes a “relatively permanent” interconnectionelement.

One example of a “readily demountable” interconnection element is theinterconnection element between rigid pins of one electronic componentreceived by resilient socket elements of another electronic component,for example, a spring-loaded LGA socket or a zero-insertion forcesocket. A second type of a “readily demountable” interconnection elementis an interconnection element that itself is resilient or spring-like ormounted in or on a spring or resilient medium. An example of such aninterconnection element is a tungsten needle of a probe card. Theinterconnection element of a probe card is typically intended to effecta temporary pressure connection between an electronic component to whichthe interconnection element is mounted and terminals of a secondelectronic component, such as a semiconductor device under test.

With regard to spring interconnection elements, generally, a minimumcontact force is desired to effect reliable pressure connection to anelectronic component (e.g., to terminals of an electronic component).For example, a contact (load) force of approximately 15 grams (includingas little as 2 grams or less and as much as 150 grams or more, perterminal) may be desired to effect a reliable electrical pressureconnection to a terminal of an electronic component.

A second factor of interest with regard to spring interconnectionelements is the shape and metallurgy of the portion of theinterconnection element making pressure connection to the terminal ofthe electronic component. With respect to the tungsten needle as aspring interconnection element, for example, the contact end is limitedby the metallurgy of the element (i.e., tungsten) and, as the tungstenneedle is made smaller in diameter, it becomes commensurately moredifficult to control or establish a desired shape at the contact end.

In certain instances, spring interconnection elements themselves are notresilient, but rather are supported by a resilient membrane. Membraneprobes exemplify this situation, where a plurality of microbumps aredisposed on a resilient membrane. Again, the technology required tomanufacture such contact elements limits the design choices for theshape and metallurgy of the contact portion of the contact elements.

Commonly-owned U.S. patent application Ser. No. 09/152,812 filed Nov.16, 1993 (now U.S. Pat. No. 5,476,211, issued Dec. 19, 1995), and itscounterpart commonly-assigned divisional U.S. patent application Ser.No. 09/397,779, filed Sep. 16, 1999, titled “Electronic AssemblyComprising a Substrate and a Plurality of Springable InterconnectionElements Secured to Terminals of the Substrate,” and U.S. patentapplication Ser. No. 09/245,499, filed Feb. 5, 1999, by Khandros, titled“Method of Manufacturing Raised Electrical Contact Pattern of ControlledGeometry,” disclose methods for making spring interconnection elements.In a preferred embodiment, these spring interconnection elements, whichare particularly useful for micro-electronic applications, involvemounting an end of a flexible elongate element (e.g., wire “stem” or“skeleton”) to a terminal on an electronic component, and coating theflexible element and adjacent surface of the terminal with a “shell” ofone or more materials. One of skill in the art can select a combinationof thickness, yield strength, and elastic modulus of the flexibleelement and shell materials to provide satisfactory force-to-deflectioncharacteristics of the resulting spring interconnection elements.Exemplary materials for the core element include gold. Exemplarymaterials for the coating include nickel and its alloys. The resultingspring interconnection element is suitably used to effect pressure, ordemountable, interconnections between two or more electronic components,including semiconductor devices.

As electronic components get increasingly smaller and the spacingbetween terminals on the electronic components get increasingly tighteror the pitch gets increasingly finer, it becomes increasingly moredifficult to fabricate interconnections including spring interconnectionelements suitable for making electrical connection to terminals of anelectronic component. Co-pending and commonly-assigned U.S. patentapplication Ser. No. 08/802,054, titled “Microelectronic ContactStructure, and Method of Making Same,” discloses a method of makingspring interconnection elements through lithographic techniques. In oneembodiment, that application discloses forming a spring interconnectionelement (including a spring interconnection element that is a cantileverbeam) on a sacrificial substrate and then transferring and mounting theinterconnection element to a terminal on an electronic component. Inthat disclosure, the spring interconnection element is formed in thesubstrate itself through etching techniques. In co-pending,commonly-assigned U.S. patent application Ser. No. 08/852,152, titled“Microelectronic Spring Contact Elements,” spring interconnectionelements are formed on a substrate, including a substrate that is anelectronic component, by depositing and patterning a plurality ofmasking layers to form an opening corresponding to a shape embodied forthe spring interconnection element, depositing conductive material inthe opening made by the patterned masking layers, and removing themasking layers to form the free-standing spring interconnection element.

Co-pending and commonly-assigned U.S. patent application Ser. No.09/023,859, titled “Microelectronic Contact Structures and Methods ofMaking Same,” describes an interconnection element having a base endportion (post component), a body portion (beam component) and a contactend portion (tip component) and methods separately forming each portionand joining the post portion together as desired on an electroniccomponent.

U.S. Pat. No. 5,613,861 (and its counterpart divisional U.S. Pat. No.5,848,685), issued to Smith et al. disclose photolithographicallypatterned spring interconnection elements formed on a substrate with abody having an inherent stress gradient formed of a resilient (e.g.,elastic) material such as chrome-molybdenum alloy or a nickel-zirconiumalloy. The stress gradient causes an end of the body to bend away fromthe substrate in the shape of an arc when the end is freed from thesubstrate.

In order to achieve the desired shape of the body, the thickness of theinterconnection element described in U.S. Pat. No. 5,613,861 must belimited. A limit on the thickness of the interconnection element limitsthe spring constant, k, of the interconnection element (kœthickness),particularly in state-of-the-art interconnection element arrays wherethe dimensions (e.g., length and width) of individual interconnectionarrays are reduced to accommodate a corresponding increase in contactpad or terminal density. A reduction of the spring constant generallyreduces the amount of load or force, F, that may be applied to resilientinterconnection elements for a given deflection, x (k=F/x). Thus, suchinterconnection elements generally cannot sustain the minimum contactforce necessary to effect reliable pressure contact to an electroniccomponent.

What is needed is a resilient interconnection element and a method ofimproving the resiliency of an interconnection element, particularlyinterconnection elements that are suitable for present fine-pitchelectrical connections and that is/are scalable for future technologies.Also needed are improved methods of making resilient interconnectionelements, particularly methods that are repeatable, consistent, andinexpensive.

SUMMARY OF THE INVENTION

An interconnection element is disclosed. In one embodiment, theinterconnection element includes a first structure of a first materialhaving a first spring constant and a second structure of a secondmaterial coupled to the first material. The first structure is capableof being free-standing by itself and the first spring constant is highenough for repeated elastic displacement without substantial plasticdeformation. The second structure can be of lithographically-patternedsecond material. Collectively, the first material and the secondmaterial have a spring constant greater than the first spring constant.In one embodiment, the interconnection element is adapted to be coupledto an electronic component to act as a conductive path for theelectronic component.

According to the invention, the spring constant of an interconnectionelement can be increased by coupling (e.g., coating) a second materialover the first material. The first material is, for example, a body ofthe interconnection element formed to have some measurable amount ofresiliency. The interconnection element of the invention increases thisresiliency by coupling a second material that itself comprises resilientproperties. The second material may also be used to increase the springconstant of a resilient interconnection. An increased spring constantpermits the interconnection element of the invention to sustain adesired contact force to effect reliable pressure contact to anelectronic component, making the interconnection element suitable foruse in a variety of applications, including as part of a densely-packedarray of interconnection elements on an electronic component to coupleto a corresponding array of contact pads or terminals on a secondelectronic component. The addition of the second structure to the firststructure will generally increase the working force for a givendeflection, but may decrease the deflection required to permanentlydeform the interconnection element. The addition of the second structuremay also increase or decrease the longevity of the interconnectionelement for a number of compression cycles to failure of theinterconnection element, depending on the material properties of thestructure material. In general, the ratios of the yield stress, a, andelastic modulus, E, of the two structures along with the thickness ofthe structures (and the total thickness of the interconnection element)will determine the final outcome.

A method is also disclosed. In one embodiment, the method includesforming a first structure coupled to a substrate, the first structurecomprising an internal stress to define a shape suitable as aninterconnection in an integrated circuit environment and coupling, suchas by coating, a second structure to the first structure to form aninterconnection element. Collectively, the first structure and thesecond structure have a strength greater than a strength of the firststructure material when used alone as an interconnection element.

The method of the invention addresses, in one aspect, enhancing thespring constant of a resilient interconnection element to make theinterconnection element suitable for use in an integrated circuitenvironment to act as a conductive path from an electronic component. Bycoupling (e.g., coating) a second structure to the first structure toimprove the spring constant of an interconnection element, the method ofthe invention addresses the limitations of the interconnection elementsformed in certain disclosures presented in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, and advantages of the invention will become morethoroughly apparent from the following detailed description, appendedclaims, and accompanying drawings in which:

FIG. 1 illustrates an interconnection element having a measurable springconstant in an undeformed free state in accordance with an embodiment ofthe invention.

FIG. 2 shows the structure of FIG. 1 after the deposition of a maskingmaterial layer over the structure in accordance with an embodiment ofthe invention.

FIG. 3 shows a planar top view of a portion of a wafer including a diehaving traces formed thereon to a central bus.

FIG. 4 shows the structure of FIG. 1 and the process of opening an areathrough the masking material layer to the interconnection element inaccordance with an embodiment of the invention.

FIG. 5 shows the structure of FIG. 1 after an opening is formed to theinterconnection element in accordance with an embodiment of theinvention.

FIG. 6 shows the structure of FIG. 1 after the coupling of a springmaterial to the interconnection element through the opening in themasking material layer in accordance with an embodiment of theinvention.

FIG. 7 shows the structure of FIG. 1 after the removal of the maskingmaterial layer to reveal an interconnection element according to anaspect of the invention.

FIG. 8 shows the structure of FIG. 1 after the coupling of a probematerial to the interconnection element through the opening in themasking material layer in accordance with an embodiment of theinvention.

FIG. 9 shows the structure of FIG. 1 after the removal of the maskingmaterial layer in accordance with an embodiment of the invention.

FIG. 10 shows the structure of FIG. 1 after the deposition of a travelstop material over the substrate in accordance with an embodiment of theinvention.

FIG. 11 shows the structure of FIG. 1 after the patterning of the travelstop and the optional step of coupling a contact material to theinterconnection element in accordance with an embodiment of theinvention.

FIG. 12 shows an embodiment of an interconnection element of theinvention making compliant contact with a contact pad or terminal of asecond electronic component.

FIG. 13 shows an interconnection element structure formed on asacrificial substrate in accordance with another embodiment of theinvention and aligned with a second substrate.

FIG. 14 shows the representation of FIG. 13 after the transfer of theinterconnection element structure to the second substrate.

FIG. 15 shows an interconnection element structure coupled to asubstrate and having a multi-layered shell in accordance with anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to interconnection elements, including contactelements. According to one aspect of the invention, the inventioncontemplates an interconnection element with improved spring propertiesover prior art interconnection elements. In another aspect, theinvention relates to improving the spring constant of prior artinterconnection elements through the coupling of additional resilientmaterial(s) to an existing interconnection element. In the eitheraspect, the invention describes an improved interconnection element overprior art interconnection elements thus improving the suitability of theinterconnection element of the invention for use in present and future,reduced-sized applications, including providing a conductive pathbetween electronic components such as in contacting and/or testing ofcontact pads or terminals of an electronic component.

Suitable electronic components include, but are not limited to, anactive semiconductor device made of any suitable semiconductor materialsuch as silicon (Si) or gallium-arsenide (GaAs), a memory chip, aportion of a semiconductor wafer, a ceramic substrate, an organicsubstrate, a printed circuit board (PCB), an organic membrane, apolyimide sheet, a space transformer, a probe card, a chip carrier,production interconnect sockets, test sockets, sacrificial members,semiconductor packages, including ceramic and plastic packages, chipcarriers, and connectors. The electronic component may be an activedevice or a passive device that supports one or more electronicconnections. The electronic component includes substrates having one ormore signal lines distributed throughout the substrate, such as aceramic, or organic substrate having a plurality of conductive signallines. distributed in individual layers of the substrate and supportingelectronic connection to one or more signal lines through contact padsor terminals exposed, for example, on the substrate. In general,suitable electronic components include, but are not limited to, devicescomprising an integrated circuit having at least two contact pads orterminals providing electrical access to the circuit. Such a device isrepresentatively demonstrated by an integrated circuit chip (ormicrochip) having a plurality of exposed contact pads or terminalsproviding access to the integrated circuit of the device.

The interconnection element of the invention may be fabricated on orindependent of the electronic component to which it is joined. In thecase of independent fabrication, the invention contemplates that theinterconnection element or elements can be fabricated with a shape,size, and metallurgy that are not limited by the materials and layoutconsiderations associated with the manufacture of the electroniccomponent. Independent fabrication also avoids the exposure of theelectronic component to the process conditions associated with formingthe interconnection element.

In one embodiment, the interconnection elements of the invention areintroduced on an electronic component (e.g., to contact pads orterminals) that is a semiconductor die or chip, preferably before thedie or chip is singulated (separated) from a semiconductor wafer. Inthis manner, a plurality of unsingulated semiconductor dies can beexercised (tested and/or “burned in”) prior to the dies beingsingulated. The interconnection elements can be configured to makereleasable (i.e., temporary) electrical connection to, for example, thetesting device, such as a probe card assembly. Such interconnectionelements can also be configured to be suitable for socketing (one formof releasable connection) electronic components, such as for performingburn-in of a die.

According to one aspect of the invention, the interconnection elementsthat are mounted to the dies and that are used to exercise the dies canbe used to make permanent connections to the dies after they have beensingulated. In this manner, it is to be appreciated that theinterconnection elements of the invention are suitable for die- orchip-scale packaging, for instance, to facilitate the connection of thedie or chip to a printed circuit board (PCB) together with or in theabsence of a die package. A detailed discussion of die- or chip-scalemounting, exercising, and packaging is presented in commonly-owned U.S.patent application Ser. No. 08/558,332, filed Nov. 15, 1995, titled“Method of Mounting Resilient Contact Structures to SemiconductorDevices,” (now U.S. Pat. No. 5,829,128, issued Nov. 3, 1998) which isincorporated herein by reference. For example, the interconnectionelements of the invention are suitable for mounting directly tosemiconductor devices, such as contact pads on a semiconductor die, forconnection with other semiconductor devices or with suitable otherelectronic components (e.g., PCBs, modules, etc.).

Disposed on an electronic component such as a space transformer of aprobe card assembly, the interconnection elements of the invention aredesigned to accommodate contact pads or terminals of electroniccomponents having very small pitch or spacing tolerances. In oneembodiment, the interconnection elements of the invention adoptalternating orientation (e.g., left-right-left-right) so as to achieve agreater pitch between their post portion than at the tip portion. Inanother embodiment, the interconnection elements of the invention adoptalternating lengths (e.g., short-long-short-long) so as to achieve agreater pitch between a post or anchor portion than at the tip portionof adjacent interconnection elements. Similarly, alternatinginterconnection elements can be fabricated to have a greater pitch attheir tip portions than their post or anchor portions. In summary, theinterconnection elements, whether fabricated on or independent of theelectronic component to which they are joined may adopt a variety oforientations to accommodate various configurations associated with theelectronic components to which they connect.

FIG. 1 shows a cross-sectional side view of structure 10 having, forexample, a plurality of spring interconnection elements similar tospring interconnection element 110. A similar interconnection element isillustrated and described in U.S. Pat. No. 5,613,861 issued to Smith etal. Reference is made to that patent for a detailed explanation of theformation of the interconnection element. The referenced patentdescribed the final structure as a spring contact or interconnectionelement. In the instant description, such a structure as described inthe referenced patent will be used as a starting point for forming animproved or enhanced interconnection element. It is to be appreciated atthis point that, as one starting point, an interconnection element orinterconnection element precursor, including but not limited to theinterconnection element described in the referenced patent, that has, inone sense, some measurable spring constant is suitable for use informing the improved interconnection element of the invention.

Interconnection element 110 of FIG. 1 comprises free portion 111 andanchor portion 112 fixed, in this embodiment, to insulating underlayer120 and electrically connected to contact pad 123. It is to beappreciated that, depending on the application, anchor portion 112 ofinterconnection element 110 may be fixed to either or both of insulatingunderlayer 120 and contact pad 123. In another embodiment contemplatedby the invention, the contact pads of an electronic component may beredistributed from one arrangement to, for example, a set of contactpads having a different arrangement and/or geometry. In such aredistribution, a layer of, for example, copper, titanium,titanium-tungsten, or other metallization may be applied over thesurface of substrate 100 and patterned as desired.

Interconnection element 110 is made of a resilient material, such as achrome-molybdenum alloy or a nickel-zirconium alloy. In one embodiment,interconnection element 110 is formed as a conductive material, althoughit is to be appreciated that the precursor can be formed of anon-conductive or semi-conductive material provided, in an applicationsuch as where the ultimate interconnection element formed from theprecursor is used as a conductive path, the interconnection element iscoated or plated with a conductive material at some point.

In one embodiment, contact pad 123 is the terminal end of acommunication line that electrically communicates with an electronicdevice formed-on substrate 100. In another embodiment, contact pad 123electrically communicates with a corresponding electronic component thatis electrically mated with free portion 111 of interconnection element110. Suitable electronic devices include, but are not limited to, atransistor, a display electrode, or other electrical device. Contact pad123 is typically made of an aluminum material, but can be made of otherconductive materials.

Insulating underlayer 120 is, for example, silicon nitride or otherpatternable insulating material. It is to be appreciated that insulatingunderlayer 120 is not necessary and can be eliminated. Insulatingunderlayer 120 and contact pad 123 are formed on or over substrate 100that is, for example, a semiconductor material, a ceramic material, aninsulating material, a polymerizable (e.g., organic) material, or acombination of such materials.

Referring to the structure described in U.S. Pat. No. 5,613,861,interconnection element 110 is formed such that a stress gradient, Δσ/h,is introduced into interconnection element 110. When interconnectionelement 110 is formed of, for example, one of the noted suitableconductive materials, the conductive material comprising interconnectionelement 110 is deposited such that tensile stress is present insuperiorly-located portions (relative to the surface of substrate 100)of the conductive material and compressive stress is present ininferiorly-located portions of the conductive material. In other words,in this embodiment, the conductive material of interconnection element110 is comprised of a plurality of layers. Alternatively, rather thandistinct layers, interconnection element 110 may itself have acontinuous stress gradient. The stress gradient causes interconnectionelement 110 to bend into the approximate shape of an arc between freeportion 111 and anchored portion 112 with free portion 111 curved awayfrom substrate 100. The approximate shape of an arc in this example hasa radius (r). In FIG. 1, theta, θ, is the angle separating the radiusline directed toward anchor portion 112 and the radius line directedtoward free portion 111. The following equation gives the approximateheight, b, of free portion 111 of interconnection element 110 fromsubstrate 100 for angles θ<50°:b=L ²/2r.L is the length of free portion 111 and r is the radius of curvature offree portion 111. One suitable height of interconnection element 110from the surface of substrate 100 to the end of free portion 111 isapproximately 6-8 mils (150-200 μm).

Since interconnection element 110 is made of a resilient material,interconnection element 110 can be displaced, in one example, in aninferiorly-directed manner toward substrate 100 at the end or contactregion of free portion 111 and deform, but will not plastically deform.In this description, interconnection element 110 is formed on asubstrate lying in an x-y plane and the referenced inferiorly-directedforce is substantially in a z-direction directed toward the surface ofsubstrate 100 (e.g., “downward”). Typically, a contact pad of anelectronic component transfers the downward force at the contact regionof free portion 111. Interconnection element 110 resists the downwardforce placed on the contact region by pushing interconnection element110 toward its original shape and, in so doing, maintains electricalcontact with the contact pad. When the force on the contact region isreleased, the interconnection element will return to its original (e.g.,arc) state, provided the force is not too great to exceed the maximumstress (i.e., yield stress) of the material and permanently deform theprecursor.

It should be appreciated that the structure shown in FIG. 1 is oneembodiment of an interconnection element with the force applied in aninferior direction toward the surface of substrate 100 by, for example,an electronic component, to displace the interconnection element. Inthis embodiment, the contact region of interconnection element 110 isthe superior surface of the end of interconnection element 110.Interconnection element 110 may alternatively be formed in a variety ofshapes having different contact regions, such as illustrated in U.S.patent application Ser. No. 08/844,946, titled “Probe Card Assembly andKit and Methods of Using the Same.” The associated contact force anddisplacement of such interconnections will similarly vary.

The formation of the interconnection element shown in FIG. 1, and asdescribed in U.S. Pat. No. 5,613,861, begins by forming contact pad 123on or over substrate 100. Additionally, insulating underlayer 120 isformed on or over substrate 100. As mentioned above, insulatingunderlayer 120 is not required and can be eliminated.

To form the interconnection element shown in FIG. 1, a layer ofconductive material is deposited adjacent substrate 100. As used herein,the deposition adjacent the substrate includes incorporation of thematerial in the body of the substrate as well as on or over thesubstate. In one embodiment, the conductive material is anickel-zirconium alloy. Part of the conductive layer is electricallyconnected directly to contact pad 123 and another portion of aconductive material is deposited adjacent insulating underlayer 120. Itis to be appreciated that there are many methods available fordepositing a conductive material such as nickel-zirconium on or over asubstrate, including electron-beam deposition, electroplating, thermalevaporation, chemical vapor deposition, sputter deposition, and othermethods.

The conductive material of interconnection element 110 can be thought ofas deposited in several sub-layers to a final thickness. U.S. Pat. No.5,613,861 describes several layers of conductive material deposited to afinal thickness of approximately one micron. A stress gradient isintroduced into interconnection element 110 by altering the stressinherent in each of the sub-layers of the conductive material.

The referenced patent instructs that different stress levels can beintroduced into each sub-layer of the conductive material that formsinterconnection element 110 in FIG. 1 by using a sputter depositionprocess. The different stress levels can be introduced in a variety ofways, including adding a reactive gas to the plasma, depositing themetal at an angle, and changing the pressure of the plasma gas. Thereferenced patent prefers introducing different stress levels by varyingthe pressure of the plasma gas, such as an argon gas. The patent furtherdescribes depositing five sub-layers of the conductive material.

After the conductive material is deposited, photolithographic patterningis employed to pattern interconnection element 110. Photolithographicpatterning is a well-known technique routinely used in the semiconductorchip industry. In one example, deposited photosensitive material is spunon top of the conductive material and soft-baked at 90° C. to drive upsolvents in the resist. The photosensitive resist is exposed to anappropriate pattern of ultraviolet light and developed. Exposed areas ofthe resist are removed during developing and the remaining resist ishard-baked at 120° C. Wet or plasma etching is then used to remove theexposed areas of the conductive material. The remaining areas of theconductive material form interconnection element 110 (a “firststructure”).

Once interconnection element 110 is formed and patterned, free portion111 of interconnection element 110 is released from the insulatingunderlayer by a process of under-cut etching. Until free portion 111 isreleased from insulating underlayer 120, free portion 111 adheres toinsulating underlayer 120 and interconnection element 110 lies flat onsubstrate 100 (indicated in dashed lines). U.S. Pat. No. 5,613,861describes two methods for releasing free portion 111 from substrate 100.In the first method, insulating underlayer 120 is pre-patterned beforeconductive layer deposition, into islands on which interconnectionelements will be formed. After the interconnection elements are formedon or over the islands of insulating underlayer 120, interconnectionelements 110 are released from insulating underlayer 120 by etching theislands with a selective etchant. In the case of an insulatingunderlayer of silicon nitride, the selective etchant is typically a HFsolution.

A second method described in the referenced patent for releasing freeportion 111 of interconnection element 110 from insulating underlayer120 is by depositing a passivating layer, such as silicon oxynitride, oninterconnection element 110 and surrounding areas of substrate 100 byplasma enhanced chemical vapor deposition (PECVD). The passivation layeris patterned into windows to expose free portion 111 of interconnectionelement 110 and surrounding areas of insulating underlayer 120. Aselective etchant, such as an HF solution, is used to etch insulatingunderlayer 120 and release free portion 111 of interconnection element110.

In this embodiment, only those areas of insulating underlayer 120 andthe free portion 111 of interconnection element 110 are under-cutetched. Anchor portion 112 of interconnection element 110 remains fixedto insulating underlayer 120 and does not pull away from insulatingunderlayer 120.

Once free portion 111 is freed from insulating underlayer 120, thestress gradient of the conductive material sub-layers that make upinterconnection element 110 cause free portion 111 to bend away fromsubstrate 100. To discourage anchor portion 112 from pulling away fromsubstrate 100, interconnection element 110 can be annealed.

U.S. Pat. No. 5,613,861 describes a final step of plating a gold layerover the outer surface of interconnection element 110 to reduce theresistance in the interconnection element. The referenced patentdescribes forming interconnection elements having a width of about10-100 microns (μm) allowing a spacing of adjacent interconnectionelements of approximately 10-20 μm on a substrate. Accordingly, thecenter-to-center distance between adjacent interconnection elements iscalculated to be approximately 20-120 μm, which is within or less thanthe typical center-to-center distance between adjacent contact pads onthe state-of-the-art chip.

As noted above, one problem with the interconnection element formed bythe referenced patent is the mechanical properties associated with itssmall dimensions. In order to accomplish the desired bending (e.g.,arcing) away from substrate 100, the thickness of interconnectionelement 110 formed according to the techniques described in U.S. Pat.No. 5,613,861 is limited. The resiliency of the interconnection elementis limited as is the spring constant. In other words, to bend far enoughto be useful as an interconnection element, interconnection element 110must be generally thin, but being thin works against high resilience andagainst a large spring constant. Thus, the interconnection elementdescribed in the referenced patent has limited practical utility for useas an interconnection element to contact pads, such as may be useful intesting of an integrated circuit chip.

The invention contemplates, in one aspect, improving the practicalutility of an interconnection element such as described in the U.S. Pat.No. 5,613,861 by improving the spring constant of the interconnectionelement. FIGS. 2-11 illustrate one process of forming an improvedinterconnection element according to the invention.

With reference to FIG. 2, starting from interconnection element 110formed on a substrate by, for example, the process described in thereferenced patent, and, in one embodiment, ignoring the final step ofplating a gold layer over the precursor, the invention deposits maskingmaterial layer 125 over substrate 100.

One problem with depositing conventional masking materials includingconventional photoresist over interconnection element 110, such as theinterconnection element formed in the referenced patent, is thatovercoating can damage or break the relatively thin (e.g., about 1micron) and fragile interconnection element. Accordingly, depositing amasking material layer over the interconnection element to pattern anopening on the interconnection element presents a challenge.

A solution to the problem with depositing a masking material over theinterconnection element such as interconnection element 110 isdepositing a positive electrophoretic resist over the structure. Asuitable electrophoretic resist material is commercially available fromthe Shipley Company of Marlborough, Mass. An electrophoretic resistworks by depositing charged particles that form masking material layer125 between an anode and cathode established about structure 10. As longas the surface of interconnection element 110 is conductive, anelectrophoretic resist deposition will deposit particles according to asubstantially uniform coating everywhere about substrate 100, includingthat area between interconnection element 110 and substrate 100. Theelectrophoretic resist will also not damage a fragile interconnectionelement.

In one embodiment, prior to the introduction of interconnection element110, conductive layer 115 of copper, titanium, or titanium-tungsten orother appropriate metal or alloy is introduced to a thickness of, forexample, about 3000 Å to 6000 Å, such as about 5000 Å over substrate 100by, for example, sputtering, to facilitate subsequent electroplatingprocessing, including the introduction of the electrophoretic resistonto substrate 100. Such a conductive layer is particularly advantageouswhen there is no convenient way to connect through the substrate. Suchmight be the case when using silicon as a substrate, or certainconfigurations of ceramic, polyimide, or other materials.

In another embodiment, contact pads on one surface are coupled tocontact pads on a second surface. Such a configuration might be utilizedin, for example, a multi-layer ceramic or other substrate. In such case,a conductive layer (e.g., shorting layer) may be introduced on thesurface opposite the surface selected to accommodate the interconnectionelement(s) of the invention. The conductive layer connects a pluralityof the contact pads to act as a generalized cathode in an electroplatingprocess. Details of materials, thickness, processing variations and thelike can be found in co-pending, commonly-owned U.S. patent applicationSer. No. 09/032,473, filed Feb. 26, 1998, titled “LithographicallyDefined Microelectronic Contact Structures,” and PCT equivalentpublished as WO 98/52224 on Nov. 9, 1998, both of which are incorporatedherein by reference.

A further alternative utilizes a redistribution layer, commonly employedto redistribute a contact pad arrangement as the conductive layer. Inone example, contact pad 123 is coupled to a redistribution layer of arouting trace and interconnection element 110 is formed at a positionaway from contact pad 123. Conductive layer 115 including, in oneexample, a routing trace maintains electrical contact with contact pad123 (or a population of contact pads 123) and/or interconnectionelement(s) 110 until the contact is no longer needed, e.g., afterelectroplating processes are completed. With respect to conductive layer115 that is a redistribution layer, there are at least the followingoptions. First, the redistribution layer remains as an intact-layeruntil late in the process when it is masked and defined to isolate thevarious traces and interconnection elements. Alternatively, theredistribution layer is patterned into traces that maintain connectionsto a central bus so that a minimal number of contacts can complete theplating circuit, which in a preferred embodiment is to theinterconnection element as cathode. Once the electroplating process(es)that is(are) used to form an interconnection element according to theinvention are complete, the connection to the common bus may be severedfor example by etching or a mechanical process such as dicing of awafer. FIG. 3 illustrates a planar top view of such a configuration(with like reference numerals representing like elements). In FIG. 3,traces 116 are patterned from contact pads 123 to central bus 126outside the edge of a chip or die of a wafer, e.g., in a scribe street.The connections of traces 116 may be severed by dicing the wafer at thescribe street.

With reference to FIG. 2, conductive material 115 is introduced adjacentsubstrate 100. Interconnection element 110 is then formed as describedabove over conductive material 115. Insulating underlayer 120 may stillbe introduced, for example, in area adjacent contact pad 123 to, in oneinstance, isolate contact pad 123.

With respect to the electrophoretic mask introduction described above,once interconnection element 110 is formed as described above, maskingmaterial layer 125 of an electrophoretic resist may then be introducedby way of an electrophoretic deposition process. A suitable thicknessfor masking material layer 125 that is an electrophoretic resist isabout 0.3 to 1 mils (8 to 30 μm). Such a mask is introduced though anelectrophoretic process to mask the substrate and expose the superiorsurface of interconnection element 110.

Another example of a masking material that is suitable for depositionover a relatively thin interconnection element that might otherwise bedamaged by traditional deposition processes including spin-on processes,is a spray-on photoresist deposited at a rate that will not damageinterconnection element 110. It is to be appreciated that a conductivelayer deposited over a portion of the substrate, including the entiresubstrate, may not be necessary in such a situation particularly wheresubsequent processing does not contemplate electroplating processing.

Once masking material layer 125 is deposited over substrate 100, FIG. 4shows the patterning of masking material layer 125 to form an opening tointerconnection element 110. In the case of a positive resist such as apositive electrophoretic resist, masking material layer 125 is exposedthrough an appropriate pattern 130 to ultraviolet light and developed.Exposed areas of masking material layer 125 are removed duringdeveloping and the remaining resist is hard-baked as known in the art.The resulting structure is illustrated in FIG. 5 having an openingthrough masking material layer 125 to expose a superior surface ofinterconnection element 110.

FIG. 6 shows the structure after the deposition of spring material 140(a “second structure”). In one embodiment, spring material 140 is aconductive material of, for example, a nickel alloy such asnickel-cobalt (e.g., 70 percent nickel-30 percent cobalt). In oneparticularly preferred embodiment, spring material 140 is deposited froma bath that may also include an additive such as saccharin. Suitablespring materials, including suitable additives are discussed in detailin co-pending, commonly-assigned U.S. patent application Ser. No.09/217,589, filed Dec. 22, 1998, titled “Method of Making a Product withImproved Material Properties by Moderate Heat Treatment of a MetalIncorporating a Dilute Additive,” and the corresponding PCT ApplicationNo. WO/99/14404, published Mar. 25, 1999, which are incorporated hereinby reference. Spring material 140 is a resilient material deposited to athickness suitable for increasing the spring constant of underlyinginterconnection element 110. In one embodiment, spring material 140 isdeposited to a predetermined thickness of, for example, about 1 mil (25μm) in thickness. Collectively, interconnection element 110 and springmaterial 140 define an interconnection element having a predeterminedspring constant greater than interconnection element 110 by itself(e.g., the spring constant generally depending in part on the dimensionsof the interconnection element). In embodiments of interconnectionelements useful in making electrical connections with, for example,contact pads or terminals of electronic components fabricated accordingto current technology, a spring constant of about 0.2 gram-force per milor greater is suitable. It is to be appreciated that the desired springconstant may vary according to the desired application such as springconstants between about 0.01 and 10 gram-force per mil and preferablyabout 0.01 and 2 gram-force per mil. These parameters are onlyillustrative as one skilled in the art can make very thin or very thickstructures with a wide range of spring constants.

In the embodiment where spring material 140 is a nickel alloy, such asnickel-cobalt, spring material 140 may be deposited by severaldeposition techniques, including but not limited to, electroplating,chemical vapor deposition, sputter deposition, and electroless plating.In one example, spring material 140 is deposited through anelectroplating process. Spring material 140 is typically applied in theform of a commercially available electroplate solution or bath. Next, acurrent is applied between interconnection element 110 and an abode ofan electroplating cell (not shown). Negative charge build-up oninterconnection element 110 causes metal ions in the electroplatingsolution to be reduced to a metallic state, coating spring material 140on interconnection element 110. It is to be appreciated that, in theexample described, interconnection element 110 is a conductive materialthat may serve as a cathode for the described electroplating process. Inan embodiment where interconnection element 110 is formed of anon-conductive material, spring material 140 is deposited, for example,by an alternative method such as noted above.

In one aspect of the invention, the enhanced interconnection elementcomprises interconnection element 110 and spring material 140. Thus,FIG. 7 shows structure 10 after removal of masking material layer 125.In the embodiment where masking material layer 125 is a photoresist,masking material layer 125 may be removed using conventional methods,such as plasma etching (e.g., oxygen ashing), laser ablation, or wetchemical etching. At this point, conductive layer 115 may also beremoved or patterned into appropriate traces via a solvent, etchingagent, or mechanical means. FIG. 7 shows conductive layer 115 removedfrom portions of the substrate, e.g., portions generally accessible byremoving agents.

With the addition of spring material 140, the composite interconnectionelement illustrated in FIG. 7 has an improved spring constant whichgenerally allows the composite interconnection element to sustain agreater contact force than interconnection element 110 increasing itsversatility in a variety of applications.

In another aspect of the invention, the interconnection is furtherenhanced by the introduction of additional material. Starting from thestructure shown in FIG. 6, FIG. 8 shows the structure after the optionaldeposition through an electroplating process of probe material 150 tothe superior surface of spring material 140. In one example, probematerial 150 reduces the resistivity of spring material 140 and providescontact metallurgy to the interconnection structure that is formed.Suitable probe materials include gold (Au), rhodium (Rh), or apalladium-cobalt (Pd—Co) alloy. In one embodiment, probe material 150 isdeposited to a thickness of approximately 30 micro-inches (7500-8000 Å)over the superior surface of spring material 140. It is to beappreciated that probe material 150 need not be deposited over theentire surface of spring material 140 but may be limited to an areacorresponding with a contact region for the interconnection element.

FIG. 9 shows structure 10 after removal of masking material layer 125.In the embodiment where masking material layer 125 is a photoresist,masking material layer 125 may be removed using conventional methods,such as plasma etching (e.g., oxygen ashing), laser ablation, of wetchemical etching. At this point, conductive layer 115 may also beremoved or patterned via a solvent, etching agent, or mechanical means.

In the embodiment described in this aspect, the enhanced interconnectionelement is a composite interconnection element comprised ofinterconnection element 110, spring material 140, and probe material150. Similar to the discussion above with respect to FIG. 7, theenhanced interconnection element illustrated in FIG. 9 generally hasimproved mechanical properties over prior art structures such asinterconnection element 110. The following processes illustrated in FIG.10 and FIG. 11 further enhance the interconnection element describedwith respect to FIG. 9. It is to be appreciated that similarenhancements can be implemented as well as with the interconnectionelement of FIG. 7.

At this point, structure 10 may be subjected to an optional heattreatment that, in one aspect, relieves stress in interconnectionelement 110, particularly at its anchor portion to secure its fixationto substrate 100, and improves the mechanical properties of springmaterial 140. Details concerning an optional heat treatment aredescribed in detail in co-pending, commonly-assigned U.S. patentapplication Ser. No. 09/217,589, filed Dec. 22, 1998, titled “Method ofMaking a Product with Improved Material Properties by Moderate HeatTreatment of a Metal Incorporating a Dilute Additive,” and correspondingPCT Application No. WO 99/14404, published Mar. 25, 1999, incorporatedherein by reference.

FIG. 10 shows structure 10 after depositing travel stop material 160over the structure. The fabrication and incorporation of various travelstops is described in co-pending, commonly-assigned U.S. patentapplication Ser. No. 09/032,473, filed Jul. 13, 1998, titled“Interconnect Assemblies and Methods,” and U.S. patent application Ser.No. 09/264,788, filed Jul. 30, 1999, titled “Interconnect Assemblies andMethods,” both of which are incorporated herein by reference. Thefollowing description sets forth one example of a suitable travel stopfor the composite interconnection element. It will be appreciated thatother travel stops described in the referenced and incorporateddocuments will generally also be suitable.

Travel stop material 160 is incorporated to limit the travel of thecomposite interconnection element when making contact with, for example,a contact pad of an electronic component. In one embodiment, the height,H, of the tip of the composite interconnection element from the surfaceof substrate 100 is approximately 5-15 mils (250-400 μm). The maximumdesired amount of deflection for the composite interconnection element,h, may be determined to be approximately 3 mils (76 μm). Thus, in oneembodiment, travel stop material 160 is deposited to a thickness ofapproximately 2-12 mils (50-300 μm) to provide a height, h, of thecomposite interconnection element over travel stop material 160 ofapproximately 3 mils (76 μm). In one embodiment, travel stop material isa non-conductive material such as a photoimageable material such as SU-8which is negative photoresist, commercially available from MicroChemCorporation of Newton, Mass. Other material for travel stop material 160includes silicon nitride or silicon oxynitride.

After the proper amount of travel stop material 160 is introduced oversubstrate 100, travel stop material 160 is patterned. In the example ofa negative photoresist, travel stop material 160 is exposed through amask such that an area around anchor portion 112 is exposed. Becausetravel stop material 160 is a negative photoresist, those areas that didnot receive an exposure due to the mask will be developed to remove thephotoresist (and the exposed portions of the photoresist will remain).FIG. 11 shows structure 10 after patterning travel stop material 160over a portion of substrate 100 including the anchor portion ofcomposite interconnection element 110A. In this embodiment, travel stopmaterial 160 will allow the deflection of composite interconnectionelement 110A towards substrate 100 with some limitation. For example,when a second electronic component is directed towards substrate 100,the electronic component will be stopped by travel stop material 160.

FIG. 11 also shows composite interconnection element 110A having anovercoating of a contact material, such as electroless or electroplatedgold coated to a few micro-inches (a few thousand angstroms) to improvethe electrical conduction properties (e.g., lower the resistance) ofcomposite interconnection element 110A. It is to be appreciated thatcoating 170 is optional in this embodiment. In the instance of anelectroplating process to introduce the overcoating a conductive layersuch as conductive layer 115 may be retained until after theintroduction, rather than removing or patterning it as described withregard to FIGS. 7 and 9, respetively.

FIG. 12 shows composite interconnection element 110A formed according tothe process described above in compliant contact with contact pad orterminal 185 of electronic component 180. Electronic component 185 isdisplaced in a z-direction toward substrate 100. Travel stop 160 limitsthe displacement and thus the deflection of composite interconnectionelement 110A. Contact region 113 of composite interconnection element110A contacts contact pad or terminal 185 to establish the electricalcontact.

The above described method relates to forming a compositeinterconnection element having improved strength characteristics overthe core interconnection element that itself has some spring constant. Astarting point was the interconnection element described in U.S. Pat.No. 5,613,861. It is to be appreciated that the invention is applicableto modifying the spring constant of a variety of interconnectionelements. The invention is suitable for interconnection elements ofvarious shapes and adopting a variety of orientations. One aspect of theinvention seeks to improve the structural characteristics (e.g., springconstant) of a resilient core. In this manner, applications andreliability of the interconnection elements of the invention can begreatly improved.

In FIG. 12, composite interconnection element 110A is described as beingcompliant in the z-direction (i.e., a z-plane). It is to be appreciatedthat composite interconnection elements are readily engineered to becompliant in more than one plane, such as compliant in a z-plane as wellas an x-y plane (parallel to the surface of substrate 100). Co-pending,commonly-assigned U.S. patent application Ser. No. 09/032,473, filedFeb. 26, 1998, titled “Lithographically Defined Microelectronic ContactStructures,” for example, describes methods of forming interconnectionelements having compliant properties in multiple planes. Suchtechniques, incorporated herein by reference, may be employed inconjunction with the techniques described herein to engineer compositeinterconnection elements with similar compliant properties.

The apparatus and method of this invention is useful in conjunction withformation of relevant structures on a sacrificial substrate. In commonlyassigned U.S. Pat. No. 5,994,142, titled “Fabricating Interconnects andTips Using Sacrificial Substrates,” a plated structure is formed on asacrificial substrate, then transferred to an electronic component. Thesacrificial substrate is removed to free the plated structure. Theremaining processing is more or less identical to that disclosed in theprimary description above. At an appropriate stage of processing, thesacrificial layer is removed, as described in the above-referenceddocument.

The apparatus and method of this invention are useful in conjunctionwith transfer of a tip structure to the instant compositeinterconnection element. Referring, for example, to U.S. Pat. No.5,829,128, and particularly to the discussion of FIGS. 8A through 8E(starting at column 37), a tip structure can be formed on a sacrificialsubstrate, then secured to the composite interconnection element (ratherthan the interconnection element 832 of that patent) in much the samemethod described in that patent. The planarizing step shown in FIG. 8C(column 38, line 59) is useful but optional in one preferredimplementation. See also co-pending, commonly assigned U.S. patentapplication Ser. No. 08/819,464, titled “Contact Tip Structures forMicroelectronic Interconnection Elements and Methods of Making Same,”filed Mar. 17, 1997, for other examples of useful tip structures.

In a similar manner, the composite interconnection element of thisinvention can be formed using a sacrificial component in place ofdirectly forming the interconnection element on substrate 100. FIG. 13and FIG. 14 illustrate a sequence where an interconnection element isformed on a sacrificial substrate and transferred to a second substrate.FIG. 13 shows sacrificial substrate 200 having interconnection element205 formed therein. For purposes of illustrating the interaction betweensacrificial substrate 200 and a second substrate, sacrificial substrate200 is illustrated as inverted. Interconnection element 205 includesfirst element portion 210 of a material with a spring constant similarto the spring constant of interconnection element 110 described above.First element portion 210 includes contact region or tip portion 207formed in substrate 205. Methods of forming contact region 207 aredescribed in U.S. Pat. No. 5,829,128, and co-pending, commonly assignedU.S. patent application Ser. No. 08/819,464, titled “Contact TipStructures for Microelectronic Interconnection Elements and Methods ofMaking Same,” filed Mar. 17, 1997, incorporated herein by reference.Alternatively, a contact region of a tip structure may be fabricatedseparately and affixed to the interconnection element as noted in U.S.Pat. No. 5,829,128.

One way to create a structure wherein an unaffixed portion curves awayfrom substrate 200 is to introduce first element portion 210 over amasking material layer and then grind, through a mechanical orchemical-mechanical polish, first element portion 210 to the desiredshape (e.g., a portion substantially parallel to substrate 205). Asecond way that the shape of first element portion 210 can be formed isforming first element portion 210 over a sloped mask. There are numeroustechniques known in the art for creating a slope on, for example, aphotoresist. One method involves the use of a gray-scale mask having agradient of opacity from clear to black. Other methods include: gentlyreflowing the masking material to form a slope; controlling the lightexposure intensity or time to the masking material; during exposure,varying the distance of the mask from the masking layer; exposing themasking layer two or more times, one through the mask having a smalltransparent area and separately with a mask having a larger transparentarea; or combinations of these methods. Methods for forming a taperedmask are described in co-pending, commonly-assigned U.S. patentapplication Ser. No. 09/032,473, filed Feb. 26, 1998, titled“Lithographically Defined Microelectronic Contact Structures,”incorporated herein by reference.

In the embodiment described, second element portion 240 of springmaterial similar to spring material 140 described above is introducedover first element portion 210. A comparison to the composite structureshown above in reference to FIG. 5 and FIG. 6 and the accompanying text,shows that second element portion 240 is introduced, in this embodiment,on the “underside” of first element portion 210.

Interconnection element 205 is coupled to sacrificial substrate 200 atan opening in sacrificial substrate 200. Interconnection element 205 iscoupled through release layer 255 such as aluminum, copper, ortitanium-tungsten deposited to a thickness of approximately 5000 Å.Overlying release layer 255 may be conductive layer 256 such as copperto facilitate the introduction of first element portion 210 by way of anelectroplating process.

FIG. 13 shows sacrificial substrate 200 aligned with substrate 300 thatis, for example, an electronic component similar to the exampledescribed in reference to substrate 100 and having contact pad orterminal. 323 formed on a surface. FIG. 14 shows substrate 300 aftercoupling interconnection element 205 to contact pad or terminal 323. Inone embodiment, interconnection element 205 is affixed at one end tocontact pad or terminal 323 by soldering or brazing then separated atrelease layer 255 from sacrificial substrate 200. In the example whererelease layer 255 is aluminum, a sodium hydroxide (NaOH) solution may beused to separate interconnection element 205. In the case of a releaselayer of copper, an etch selective for copper may be used to separateinterconnection element 205 from release layer 255. A grinding proceduremay be necessary at this point to planarize a superior surface of firstelement portion 205 (and any remaining conductive layer 256).

Third element portion 250 similar to probe material 150 (FIG. 11) maythen be introduced over first element portion 110 by, for example,electroless plating. A travel stop and contact material overcoat may beincorporated following a similar procedure as discussed above withreference to FIGS. 10 and 11 and the accompanying text.

The apparatus and method of this invention can be formed in a way toprovide controlled impedance nearly to the contact region of thecomposite interconnection element. A useful controlled impedancestructure is described in U.S. Pat. No. 5,829,128 at column 17, line 35,and illustrated in FIG. 2B of that patent. A comparable controlledimpedance structure is described in U.S. Pat. No. 5,917,707 andillustrated in FIG. 12 of that patent. These patents list usefulmaterials and processing techniques for such structures.

An analogous structure can be formed using the instant compositeinterconnection element as illustrated in FIG. 13. In FIG. 13, contactpad 323 is analogous to contact pad 123, insulating layer 320 toinsulating layer 120, interconnection element 310 to interconnectionelement 110, spring material 340 to spring material 140, and probematerial 350 to probe material 150, described above with reference toFIG. 7 and the accompanying text. Beginning, in one embodiment,referring to FIG. 13, from the structure illustrated in FIG. 7,insulating material 335 is applied over some portion of the compositeinterconnection element, and conducting material 345 is applied oversome portion of insulating material 335. In a preferred embodiment,insulating material 335 is applied over probe material 350. Insulatingmaterial 335 can be, for example, PARALENE® (commercially available fromE.I. DuPont de Nemours Co. of Wilmington, Del.) or other suitableinsulating material introduced to a suitable thickness of, for example,0.1-3 mils. Insulating material 335 is selectively applied so as not topreclude electronic connection of the interconnection or conductingmaterial 345. Conducting material 345 may be applied in a variety ofmethods. In one preferred embodiment, conducting material 345 is appliedby sputtering. In one preferred embodiment, conducting material 345 isgold. Conducting material 345 is in contact with trace 355, which inturn is connected to a suitable voltage level. In one preferredembodiment, trace 355 is held at ground. A plurality of such conductingmaterial 345 elements can be connected together, and differentpluralities may be held at the same or different voltage levels. Theexact dimensions of conducting material 345 can be selected by oneskilled in the art. One useful shape of conducting material 345 isapproximately identical in top view to the top view of the compositeinterconnection element except for exposed contact region 365.Conducting material 345 can partially or even completely surround theinterconnection element, provided that sufficient insulation is providedand that contact region 365 remains exposed to establish a connection.

One useful variant of this structure is to have the interconnectionelement described above with reference to FIG. 7 provide the mechanicalsupport only, and have conducting material 345 carry an electricalconnection of interest. In this case, the interconnection element wouldbe held to a suitable voltage level and conducting material 345 wouldcarry the electrical connection of interest, such as a signal, clock,data, address, control, or power for a given interconnection. In thisembodiment, insulating material 335 could entirely cover theinterconnection element. Contact region 365 would be part of conductingmaterial 345 rather than part of the interconnection element describedabove with reference to FIG. 7.

In the preceding detailed description, the invention is described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the claims. The specification and drawings are, accordingly, tobe regarded in an illustrative rather than a restrictive sense.

1. A method of forming an interconnection element comprising: forming afree-standing first structure coupled at a first end to a firstsubstrate, a second end of the free-standing first structure spaced awayfrom the substrate and being free to flex toward the substrate, thefirst structure comprising a first material and having a first springconstant; applying a masking material to the free-standing firststructure while the first structure is free standing with the second endspaced away from the substrate and free to flex toward the substrate;and coating on the free-standing first structure a second structure of asecond material through an opening in the masking material on the firststructure, the first structure and the second structure comprising theinterconnection element and the interconnection element having a springconstant greater than the spring constant of the first structure.
 2. Themethod of claim 1, wherein coating the second structure comprisesoverlying a portion of the first structure.
 3. The method of claim 1,wherein the substrate is a first substrate, the method furthercomprising transferring the interconnection element from the firstsubstrate to a second substrate.
 4. The method of claim 1, whereincreating the free-standing first structure further comprises forming apre-release structure having a base coupled to the structure and a freeend extending over a portion of the substrate; and releasing the freeend from the first substrate to form a cantilever.
 5. The method ofclaim 1, further comprising transferring the interconnection element toa second substrate.
 6. The method of claim 1, wherein the maskingmaterial is an electrophoretic resist.
 7. The method of claim 1, whereinthe first spring constant is sufficient for repeated elasticdisplacement of the first structure without substantial plasticdeformation of the first structure.
 8. The method of claim 1, furthercomprising using the interconnection element to test an electroniccomponent.
 9. The method of claim 1, further comprising removing themasking material.
 10. The method of claim 1, further comprising couplinga probe material to the second material through the opening of themasking material.
 11. The method of claim 10, further comprisingremoving the masking material.
 12. The method of claim 1, furthercomprising fabricating a travel stop for the interconnection element.13. The method of claim 1, further comprising depositing an overcoatingof contact material over the interconnection element.